Photonic crystals have applications in reducing the size of passive waveguide components and potentially leading to new photonic structures such as switches. Photonic crystals may be two dimensional where the photonic crystal and forbidden gap are formed in a single plane or three dimensional where the forbidden gap is formed in two orthogonal planes. Photonic crystals in two dimensions are comparatively easy to fabricate but are lossy because confinement by the two dimensional crystal is only provided in a the single plane. Despite the shortcomings of two dimensional photonic crystals, they are generally viewed as the only way to integrate photonic crystals on semiconductor substrates. Relatively little effort is currently spent on making three dimensional photonic crystals which are typically formed from polycrystalline silicon bars. Polycrystalline silicon has good optical properties with nxcx9c3.1 and kxcx9c0. Polycrystalline silicon is formed using low pressure chemical vapor deposition (CVD) which is typically operating at temperatures of about 700 degrees Celsius (C) or higher and has a minimum growth temperature of about 600 degrees Celsius. These relatively high temperatures make it difficult to integrate photonic crystals with integrated circuit technology and increase the thermal stress between the substrate and the photonic crystals and are too high for substrates containing aluminum or III-V materials. Typical photonic crystal fabrication relies on micromachining and optics technologies.
In accordance with the invention, polycrystalline silicon may be replaced by hydrogenated amorphous silicon (a-Si:H) or non-hydrogenated amorphous silicon (a-Si) as a material for fabrication of photonic crystals. Non-hydrogenated amorphous silicon has somewhat higher electromagnetic losses than hydrogenated amorphous silicon. Hydrogenated amorphous silicon or non-hydrogenated amorphous silicon may be formed by plasma enhanced chemical vapor deposition (PECVD) or sputtering, neither of which is dependent on thermal activation.
Hydrogenated amorphous silicon may have its optical properties engineered by controlling the hydrogen content or by substituting elements for Si. Non-hydrogenated amorphous silicon (a-Si) may have its optical properties engineered as well by substituting elements for Si. Reduction of the deposition temperature to the range of about 225-330xc2x0 C. as disclosed in U.S. Pat. No. 6,436,488 and incorporated by reference, reduces the thermally induced stresses between a-Si:H and the substrate. The reduction in deposition temperature substantially expands the choice of substrates. Compatibility with a wide range of substrates such as silicon, GaAs, InP and glass allows the technology to be used with a variety of devices enabling economies of scale and allows photonic crystals to be integrated into integrated circuit technology.